Cooling fan with internally tapered housing

ABSTRACT

A cooling fan includes a fan housing and a rotor. The fan housing includes an inner surface defining an inner space therein. The inner surface expands along a direction parallel to a central axis of the fan housing. The rotor is received in the inner space and surrounded by the inner surface of the fan housing. The rotor includes a hub and a plurality of rotary blades extending outwardly from the hub. Each of the rotary blades has an outer edge confronting the inner surface of the fan housing. The outer edge of each rotary blade slants towards the central axis of the fan housing.

BACKGROUND

1. Technical Field

The present disclosure relates generally to cooling fans, and moreparticularly to an axial fan with a fan housing which can be easilyfabricated.

2. Description of Related Art

Cooling fans are commonly used in combination with heat sinks forcooling electronic components, such as CPUs. Normally, the heat sink isarranged on the electronic component to absorb heat therefrom, while thecooling fan is arranged on the heat sink to produce forced airflowflowing through the heat sink to take away the heat.

Generally, the cooling fan includes a stator, a rotor rotatablysupported by the stator, and a fan housing surrounding the rotor forguiding the forced airflow through the heat sink. The fan housingusually has a rectangular or annular profile. An inner surface of thefan housing facing the rotor is cylindrical, to avoid interference ofthe rotor and the fan housing during rotation of the rotor. The fanhousing is usually made of plastic, by a process of injection molding.During the molding process, after the fan housing is molded in a mold,it is difficult to separate the fan housing from the mold because theinner surface of the fan housing is cylindrical. As a result, the fanhousing is liable to sustain abrasion of the inner surface thereofand/or deformation during the removal process.

What is need, therefore, is a cooling fan which can overcome the abovelimitations.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing is a cross-sectional view of a cooling fan according to anexemplary embodiment.

DETAILED DESCRIPTION

The drawing shows a cooling fan according to an exemplary embodiment,the cooling fan including a fan housing 12, a stator 20, a rotor 14, anda pair of bearings 129.

The fan housing 12 is annular (or cylindrical) and hollow. An air inlet121 is formed at a top of the fan housing 12, and an air outlet 123 isformed at a bottom of the fan housing 12 opposite to the air inlet 121.The fan housing 12 has an inner surface 124 surrounding the rotor 14.The inner surface 124 converges (tapers) slightly in a downwarddirection, i.e., the inner surface 124 of the fan housing 12 slantstowards a central axis O of the fan housing 12 from top to bottom. Putanother way, the inner surface 124 of the fan housing 12 expandsslightly in an upward direction away from the central axis O of the fanhousing 12, with an inner space 126 surrounded by the inner surface 124correspondingly expanding slightly in the upward direction. Accordingly,the air inlet 121 at the top of the fan housing 12 is a little largerthan the air outlet 123 at the bottom of the fan housing 12.

Since the inner surface 124 of the fan housing 12 expands upwardly alongthe central axis O, after the fan housing 12 is molded in a mold, it isrelatively easy to separate the fan housing 12 from the mold by movingthe mold in an upward direction along the central axis O of the fanhousing 12. Furthermore, during the separation process, friction betweenthe inner surface 124 of the fan housing 12 and the mold is avoided.Thus the quality of the fan housing 12 obtained should be good. In orderto maintain the cooling capability of the cooling fan and stillfacilitating separation of the fan housing 12 from the mold, a firstangle θ1 between the inner surface 124 and the central axis O of the fanhousing 12 is in the range of 0.3˜3 degrees.

A base 125 is received in the fan housing 12, and is arranged at the airoutlet 123. A central tube 128 extends upwardly from a center of thebase 125. A central hole 30 extends through the central tube 128, suchthat top and bottom ends of the central tube 128 are open. That is, thecentral hole 30 is a through hole. In addition, an annular recess 32communicating with the central hole 30 is formed at an inner peripheryof each of the top and bottom ends of the central tube 128. Each recess32 has a diameter exceeding that of the central hole 30. Thus the topand bottom ends of the central tube 128 have an inner diameter exceedingthat of a middle portion of the central tube 128.

The stator 20 is mounted around the central tube 128 of the base 125.The stator 20 includes a stator core 22 with coils 24 wound thereon toestablish an alternating magnetic field, and a PCB (printed circuitboard) 26 electrically connected with the coils 24 to control electricalcurrent flowing through the coils 24.

The rotor 14 includes a hub 146 forming a shaft seat 147 at a centralportion thereof, a plurality of rotary blades 142 extending radially andoutwardly from an outer periphery of the hub 146, a magnet 148 adheredto an inner surface 124 of the hub 146 and facing the coils 24 of thestator 20, and a shaft 144 extending downwardly from the shaft seat 147of the rotor 14. The shaft 144 defines an annular notch 140 at a distalend thereof.

Each of the rotary blades 142 has an outer edge 145 confronting theinner surface 124 of the fan housing 12. The outer edge 145 of eachrotary blade 142 is approximately parallel to the inner surface 124 ofthe fan housing 12. That is, the outer edge 145 of the rotary blade 142slants towards the central axis O of the fan housing 12 from top tobottom. A second angle θ2 between the outer edge 145 of the rotary blade142 and the central axis O of the fan housing 12 is equal to the firstangle θ1 between the central axis O and the inner surface 124 of the fanhousing 12. Thus a distance between the outer edge 145 of the rotaryblade 142 and the inner surface 124 of the fan housing 12 is constantfrom top to bottom.

As shown in the drawing, a height of the outer edge 145 of the rotaryblade 142 as measured parallel to the central axis O of the fan housing12 is designated as H, a first distance between a bottom end of theouter edge 145 of the rotary blade 142 and the central axis O of the fanhousing 12 is designated as R1, and a second distance between a top endof the outer edge 145 of the rotary blade 142 and the central axis O ofthe fan housing 12 is designated as R2. The second distance R2 isslightly larger than the first distance R1, and the second angle θ2between the outer edge 145 of the rotary blade 142 and the central axisO should satisfy the equation: ^(θ) 2=tan⁻¹((R2−R1)/H).

The bearings 129 are received in the top and bottom recesses 32 of thecentral tube 128, respectively, and surround the shaft 144. Whenassembled, the rotor 14 is received in the inner space 26 and surroundedby the inner surface 124, with the shaft 144 extending through thebearings 129. Thus the shaft 144 of the rotor 14 is rotatably supportedby the pair of bearings 128. A locking ring 40 is arranged in the bottomrecess 32 of the central tube 128 and engages in the notch 140 of theshaft 144 to limit movement of the shaft 144 along an axial directionthereof. A coil spring 50 is arranged between the bottom bearing 129 andthe central tube 128 for applying a preset engaging pressure between therotor 14 and the top bearing 129, thereby ensuring that the top bearing129 remains stationary relative to the hub 146 in the axial direction ofthe shaft 144.

During operation, the rotor 14 is rotated by the interaction of thealternating magnetic field established by the stator 20 and the magneticfield of the magnet 148 of the rotor 14. The rotary blades 142 thusproduce forced airflow to take away heat generated in an applicationenvironment that employs the cooling fan. Since the distance between theouter edge 145 of each rotary blade 142 and the inner surface 124 andthe fan housing 12 is uniform from top to bottom, during rotation of therotor 14, interference of the rotor 14 and the fan housing 12 isavoided, and the cooling fan can operate smoothly and quietly.

It is to be understood, however, that even though numerouscharacteristics and advantages of embodiments have been set forth in theforegoing description, together with details of the structures andfunctions of the embodiments, the disclosure is illustrative only, andchanges may be made in detail, especially in matters of shape, size, andarrangement of parts within the principles of the disclosure to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

1. A cooling fan comprising: a rotor comprising a hub and a plurality ofrotary blades extending outwardly from the hub; and a fan housingsurrounding the rotor, the fan housing having an inner surfaceconfronting the rotor, the inner surface expanding along a directionparallel to a central axis of the fan housing.
 2. The cooling fan ofclaim 1, wherein an angle defined between the inner surface of the fanhousing and the central axis of the fan housing is in the range of 0.3˜3degrees.
 3. The cooling fan of claim 1, wherein each of the rotaryblades comprises an outer edge confronting the inner surface of the fanhousing, the outer edge of each rotary blade aslant towards the centralaxis of the fan housing.
 4. The cooling fan of claim 3, wherein an angledefined between the outer edge of each rotary blade and the central axisof the fan housing is in the range of 0.3˜3 degrees.
 5. The cooling fanof claim 3, wherein the outer edge of each rotary blade is parallel tothe inner surface of the fan housing.
 6. The cooling fan of claim 1,wherein the fan housing defines an air inlet and an air outlet atopposite sides, the air inlet being larger than the air outlet.
 7. Thecooling fan of claim 6, wherein the inner surface of the fan housingexpands from the air outlet towards the air inlet.
 8. The cooling fan ofclaim 7, wherein each of the rotary blades comprises an outer edgeconfronting the inner surface of the fan housing, a first end of theouter edge adjacent to the air outlet being closer to the central axisof the fan housing relative to a second end of the outer edge adjacentto the air inlet.
 9. The cooling fan of claim 7, wherein each of therotary blades comprises an outer edge confronting the inner surface ofthe fan housing, the outer edge of each rotary blade parallel to theinner surface of the fan housing.
 10. The cooling fan of claim 9,wherein an angle defined between the inner surface of the fan housingand the central axis of the fan housing is in the range of 0.3˜3degrees.
 11. The cooling fan of claim 7, wherein an angle definedbetween the inner surface of the fan housing and the central axis of thefan housing is in the range of 0.3˜3 degrees.
 12. A cooling fancomprising: a fan housing having an inner surface defining an innerspace therein, the inner surface expanding along a direction parallel toa central axis of the fan housing; and a rotor received in the innerspace and surround by the inner surface of the fan housing, the rotorcomprising a hub and a plurality of rotary blades extending outwardlyfrom the hub, each of the rotary blades having an outer edge confrontingthe inner surface of the fan housing, the outer edge of each rotaryblade aslant towards the central axis of the fan housing.
 13. Thecooling fan of claim 12, wherein an angle defined between the innersurface of the fan housing and the central axis of the fan housing is inthe range of 0.3˜3 degrees.
 14. The cooling fan of claim 12, wherein anangle defined between the outer edge of each rotary blade and thecentral axis of the fan housing is in the range of 0.3˜3 degrees. 15.The cooling fan of claim 12, wherein the outer edge of each rotary bladeis parallel to the inner surface of the fan housing.
 16. The cooling fanof claim 15, wherein an angle defined between the inner surface of thefan housing and the central axis of the fan housing is in the range of0.3˜3 degrees.